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Cell division in eukaryotes involves a complex self-organization process that drives the transient assembly of dynamic microtubules into a bipolar spindle around the chromosomes to segregate them to the two daughter cells. Spindle shape and size do not depend on the initial spatial organization of the chromatin, but are determined by microtubule motor activities.
Kinesins conventionally act as molecular motor proteins that translocate along microtubules. However, several kinesins also control microtubule polymerization dynamics. New work shows that the yeast kinesin-8 Kip3p has a unique combination of plus-end motor and plus-end depolymerase activities. These activities facilitate the positioning of the mitotic spindle at the cell cortex.
Cool-1 was previously identified as an effector of activated Cdc42 and as a regulator of epidermal growth factor receptor (EGFR) trafficking. Cool-1 has now been shown to be a phosphorylation-dependent activator of Cdc42 that contributes to transformation by Src, thus proving to be an unusually versatile signalling protein.
A new study shows that alveolar macrophages use the cystic fibrosis transmembrane-conductance regulator (CFTR) to maintain lysosomes at low pH and to restrict the growth of ingested bacteria. This may help to explain the persistent infections and chronic inflammation of the lungs that characterize cystic fibrosis.
During anaphase, the cysteine protease separase cleaves cohesin and releases sister chromatids. In budding yeast, separase also has a crucial non-proteolytic role in triggering mitotic exit. Separase performs a similar non-catalytic function in frog and mouse oocytes through its physical interaction with cdk1. Vertebrate separase is therefore essential not only for homologue disjunction, but also for bringing about the end of meiosis I.
